1NIRI with Altair has been measured to have radial barrel distortion at f/32. This is most prominent for programs performing large offsets. The formula for removing the distortion is r' = r + k*r*r, where k = (1.32 +/- 0.02) * 10^-5 . r is the uncorrected distance from the field center in pixels and r' is the corrected distance from the center in pixels. Thus, at a distance of 500 pixels from center, an object will appear about k*500*500 = 3 pixels closer to the center of the array than reality. PIs interested in high-precision astrometry are encouraged to contact either the NIRI or Altair instrument scientists to discuss this issue.